Extended work schedules almost invariably result in reduced time for sleep. Work schedules that produce the shortest sleep times are those of night workers. In addition to sleep loss, shift work also results in chronic maladaptation of circadian rhythms. Recent studies have demonstrated that sleep loss has an adverse health impact and may represent a risk factor for obesity, hypertension and diabetes. Whether circadian maladaptation, independently of sleep loss, also has negative health consequences is not known. The overall goal of the present proposal is to test the hypothesis that sleep loss as occurs during extended work schedules may result in adverse health consequences. We propose to use two experimental protocols, each involving 8 days of bedtime curtailment to model in the laboratory the amount of sleep loss typically associated with extended work schedules. The first protocol simulates a schedule of regular extended daytime hours and restricted nighttime sleep. The second protocol simulates a work schedule alternating between day work and night work. The total number of bedtime hours during the experimental period is identical in both models and, because of the restricted bedtimes (5 hours), it is expected that the total amount of sleep occurring during the 8-day experimental period will be similar in both models. Glucose tolerance, neuroendocrine profiles, cardiovascular function, and neurobehavioral parameters will be measured under baseline conditions and at the end of the 8-day experimental period. Two groups of gender- and age-matched healthy subjects will be studied under each protocol in order to allow for the testing of gender differences and impact of circadian disruption independently of sleep loss. The results of the proposed studies are expected to provide an estimation of sleep loss and circadian disruption as risk factors for the health and well-being of many Americans who work long and/or irregular hours.